Connecting transmitters to vacuum-tube amplifiers



|. B. CRANDALI..

CONNECTIUG TRAUSMITTERS T0 VACUU=N1TUBEAMPLIFIERS.

' V APPLICATION HLED ocT.13.'1911. v 1,422,837. Patented July 18, 1922,u

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IRV'ING- B. CRANDALL, 0F NAHANT, MASSACHSETTS, .ASSIGNOR T0 WESTERN ELEC- Tmc COMPANY, INCORPORATED, or Yoan. l

NEW YORK, N. Y., A CORPORATION OF NEW CONNECFTING TRANsMrrTERs To vacuum-TUBE AMPLIFIEBs.

Specification of Letters Patent.

Patented July i8, 11922.

Application filed October 13, 1917. Serial No. 196,389.

T 0 all/w 710m it may concern.

Be ritlmown that I, IRVING B. CRANDALL, a citizen. of the United States', residing at Nahant, in the county of Essex and State of Massachusetts, haveinvented certain new and" useful Improvements in Connecting Transmitters to Vacuum-Tube Amplifiers, of which the following is a full, clear, concise, and eXact description.

This invention relates to means and methods of connecting a transmitter to a vacuum tube amplifier.

The invention in its generic aspect anticipates the use of either a condenser transmitter or a microphone transmitter, but is particularly adapted to the former case.

Special objects of the invention are to simplify the circuits and reduce the amount of battery required for the operation of such a combination of transmitter and amplifier. When a condenser transmitter is used this is accomplished by using a single battery or source of electrical energy for the two purposes of charging the transmitting condenser and operating the associated vacuum tube, and when a microphone transmitter is used the battery energizes the microphone and operates the vacuum tube.

In the accompanying drawings, Fig. 1 represents diagrammatically an arrangement of the invention; Fig. 2, a modified arrangement, Figs. 3 and 4 represent multi-stage amplifier circuits corresponding to Figs. 1 and 2 respectively, in which a single high voltage battery is used for the double purpose of charging the condenser and operating the vacuum tubes and Fig. 5 shows an arrangement in which a microphone transmitter is used.

Referring specifically to Fig. 1,.'1 is a condenser transmitter which consists essentially in a condenser, one of whose plates t is free to vibrate under the influence of sound waves and' thereby change .the electrical capacity of the condenser. Such transmitters are known in the art. One

. plate t of transmitter T is connected to the .a battery E, which portion may be adjusted according. to the potential desired across the plates of the condenser T. Plate t is also connected through a high resistance R to the filament, while between resistance R and the filament is connected the usual battery A. The output circuit of the vacuum tube amplifier contains the battery E, a transformer coil 2 and a resistance r which symbolizes the resistance of the output circuit.

In operation the battery E thus acts as a source of potential for charging the condenser transmitter T, and at the same time furnishes the current for the output circuit of the vacuum tube amplifier. When sound waves impinge upon the late t and cause it to vibrate, a correspon( ing variation -in the potential across the filament and grid occurs, which causes a corresponding variation of current in the output circuit. These variations are impressed upon a transmission line 4 through any suitable means, as a transformer 2.

In Fig. 2 is illustrated a form of my invention in which the condenser T is arranged to have the potential of the battery E impressed thereon by havino its plates connected to the filament and ptlate respectively of the vvacuum tube device. This form operates most satisfactorily in case the resistance R and the reactance of the condenser T are of considerably larger magnitude than the output resistance r and the internal resistance of the tube.

The multi-stage amplifier circuits of Figs. 3 and 4 correspond to the arrangements of Figs. 1 and 2 respectively, but differ in that the process of amplification is repeated by using the output circuit of the first tube to produce an increased variation of potential upon the filament and grid of a second tube l. The same battery E serves to operate the several vacuum tubes of each series and also to impress a proper potential upon the plates of the transmitter T. In Fig. 3, however, a suitable portion ofthe battery Eis connected across the transmitter T to energize it, while a less portion is connected into the output circuit. The respective amounts are adjustable, as shown. The battery arrangements of Figs. land 3 are mutually interchangeable. The choice of sistances r', r2 are connected with the outamplifier. Re#

put circuits of each vacuum tube device,

while the charging of condensers c, c serves.

r', r2. The arrangement of Fig. 4 is related to that of Fig. 3 as Fig. 2 is to Fig. l and operates well when the resistance R and reactance of transmitter T are of large magnitude compared to 1" and the internal resistance of the tube l.

In operation a difference of potential impressed upon the plate t, t of the order of 100 or 200 volts would give good'results, but this invention is in no wise limited to any such values. rlhe transfer of charge along conductor 3 is a minute lcurrent of sound wave frequency and of comparably high voltage. This current is greatly amplified by the vacuum tube device l, the resistance R being of such value that no appreciable discharge of the condenser shall take place therethrough in the time necessary for the diaphragm or plate t to make one vibration. Although in Figs. l and 2 the amplified current is impressed through a transformer 2 upon a transmission line 4:, the invention is not so limited and the amplified current may be further amplified, transmitted with or without such amplification by wire or radio transmission, or put to Such other use as desired. The device 1 may consist of any suitable vacuum tube, thermionic amplifier or electron discharge device.

The arrangement of Fig. 5 is intended to be used where a microphone transmitter, across which it is desirable to impress a comparatively high voltage, is used, since the battery E is ordinarily of such a voltage. It could be used where'a low potential is desired, but would not be much more economical thanl the use of an independent transmitter battery. An adjustable connection is made to battery .E so that a suitable voltage is produced for the circuit of the microphone M. Sound waves produce variations of current therethrough, which are impressed upon the amplifier through the primary P and secondary S of a transformer. T e battery A and resistance R are similar to the corresponding battery and resistance of the arrangement in Fig. l and perform similar functions. Battery E performs the double function of furnishing current to the transmitter and the amplifier.

What is claimed is:

l. In. a device for producing amplified electrical waves corresponding to sound waves, a condenser whose capacity is variable in response to sound waves, a source of electrical potential for maintaining the electrodes of said condenser at a different relative potential, means for impressing the alternating current due to said variation of capacity upon an amplifying device, said amplifying device being supplied with operating current by said source of electrical potential.

2. In combination, a transmitter for changing sound waves into waves of electrical current, an amplifier for said current waves, and a common source of electrical energy arranged to energize said transmitter and to furnish operating current for said amplifier.

3. In combination, a transmitter for changing sound waves into electrical waves, an amplifier for said electrical waves, Vand a common source of electrical potential for polarizing said transmitter and supplying operating current to said amplifier.

4. In combination, a transmitter for changing sound waves into electrical waves,

an amplifier for said electrical' waves which produces corresponding waves of greater energy and a common source of electrical p0- tential for energizing said transmitter and supplying operating current to said amplifier.

5. In combination, a device having electrical capacity, an element in said device f ree to vibrate, the vibrations thereof causing Variations of electrical capacity in said device corresponding to the said vibrations, a source of electrical energy for charging said capacity, said variations of electrical capacity causing a varying currentin a conductor, an amplifier for said current, said source of electrical energy furnishing operating current for said amplifier.

6. In a device for transforming sound waves into electrical waves of considerable amplitude, an electrostatic transmitter whose electrodes are respectively connected to the filament and grid of athree-element thermionic amplifier, a source of continuous electrical potential between said filament and the electrode connected thereto, a comparatively high resistance connecting said other electrode with said source of potential at a point electrically nearer said filament than the point of connection of said first-named electrode, said source of electrical potential being located in a circuit between the lament and the third element of said thermionic device.

7. In a device for transforming sound waves into amplified electrical waves, a transmitter connected in series with a source of potential and two elements of a thermionic device, a comparatively high resistance shunting said elements, said source of potential being connected serially in the output circuit of said thermionic device.

8. Means for transforming sound waves into amplified electrical waves including a transmitter connected in circuit with a source of electrical energy and two elements of a thermionic amplifier, a resistance shunting said two elements, said source'of potential. 130

being in circuit with one of said elements and a third element of said thermionic amplier.

9. In a system for producing amplified electrical Waves, a condenser Whose capacity is variable in response ,to sound waves, a source of electrical potential for maintaining a potential difference across the electrodes of said condenser, means for impressing the Waves due to said variation of capacity upon an amplifyingl device,\the output circuit of said amplifying device being electricallyy connected to the input circuit of a second amplifying device, said source of electrical potential being in. circuit with the output circuit of each of said amplifying device so as to furnish the current therefor.

10. In combination', a transmitter for changing sound Waves into Waves of electrical current, an amplier for said current Waves, a common source of electrical potential connected to energize said transmitter and to furnish operating current for said amplifier, said source having an adjustable connection to one of said devices so that a part only thereof is used.

11. In combination, a transmitter for causing Waves of electrical current corresponding to sound Waves, an amplifier for said current, a source of electrical energy for said amplifier, a portion of said source being connected across said transmitter.

In Witness whereof, I hereunto subscribe my7name this 10th day of @ctober A. D., 191

IRVING B. CRANDALL. 

